On-chip sample preparation for whole blood analysis

ABSTRACT

A novel filter-less separation technique for separating suspended particles from a solution is disclosed. More specifically, an on-chip bioparticle separator is disclosed, which relies on the differential force exerted by application of a series of high magnitude, short duration pressure pulses on bioparticles in suspension within microchannels, resulting in separation of suspended bioparticles. The filter-less separation technique is inherently suited to μTAS (Micro Total Analysis System) since it exploits uniquely microscale phenomena to achieve separation. The on-chip bioparticle separator can be easily integrated with a disposable biochip, can be fabricated using low-cost, rapid manufacturing techniques, and can provide high performance for separation of bioparticles without the use of specialized or expensive equipment. Embodiments of the present invention address a significant challenge in the development of disposable microfluidic biochips, specifically, providing a reliable solution for separating bioparticles in a microfluidic system that may be immediately applied for a variety of microfluidic biochip applications.

CROSS-REFERENCE TO RELATED APPLICATIONS/INCORPORATION BY REFERENCE

This application is a divisional application of U.S. patent applicationSer. No. 10/946,685 and claims priority to provisional U.S. PatentApplications Ser. Nos. 60/506,641; 60/506,226; 60/506,321; 60/506,424;and 60/506,635 all filed on Sep. 26, 2003, and all of which areincorporated herein by reference in their entirety.

This patent application incorporates U.S. Ser. No. 10/946,818 herein byreference in its entirety.

TECHNICAL FIELD

Embodiments of the present invention generally relate to the developmentof filter-less separation techniques for separating blood cells andplasma from a whole blood sample. This technique can be applied toseparation of microparticles (or microspheres) from a particle-ladenliquid by applying a series of pressure pulses to a suspended solution.This approach is particularly relevant for lab-on-a-chip applicationswherein conventional separation processes such as centrifugation orfiltering are difficult to implement.

BACKGROUND OF THE INVENTION

Microfiuidic systems for biochemical analysis are generally composedbroadly of the following components: fluid channels to guide fluid flow,microvalves to regulate fluid flow, a pressure source to cause fluidicdisplacement, and biosensors to detect relevant parameter. Biosensorsare biological sensors which, depending on their application, measure aparticular parameter in a bodily fluid such as blood.

An analyte frequently in use for various diagnoses, blood, is anon-Newtonian fluid transporting oxygen, carbon dioxide, nutrients,salts, hormones, metabolites and various other components. The mostimportant components of blood, from a rheological point of view, areplasma and RBC's (red blood cells). RBC's take up about half the volumeof whole blood and significantly impact the flow characteristics ofblood. Blood plasma thus accounts for about half the volume of wholeblood. The plasma itself is about 95% (w/w) water. The rest is proteins,minerals, vitamins, glucose etc.

Quite often, biosensors need to deal with irrelevant or unwantedcomponents in the sensed solution. For example, in a microfluidic deviceto measure blood glucose level, the sensor where the electrochemicalreaction takes place frequently experiences interference frommicroparticles like red blood cells, thereby reducing its efficiency andpossibly increasing reaction time. In other cases, the microparticlesmight cause interference during detection by optical means due toobstruction of projected light. The separation of these microparticlesfrom the remainder of the suspension solution is thus often desirable.

The most common methods in use to achieve separation of bioparticles, inlab-on-a-chip or μTAS systems, have been physical filtration and lesscommonly, centrifugation. U.S. patents USRE31688, U.S. Pat. No.5,914,042, U.S. Pat. No. 5,906,570, and U.S. Pat. No. 4,619,639,incorporated in their entirety by reference herein, describe some of thedifferent types of membrane filtration methods. The underlying principlein this technique is to cause separation of blood into its constituentsby making it flow through a membrane filter with a number of poreshaving micrometer-range dimensions. According to the purpose of thedevice, the pore size of the membranes is varied, ranging fromapproximately, 0.5 micron diameter to 5 micron diameter. In the case ofa very small pore size, some positive pressure might be required to makethe solution cross the membrane. There are a number of membranematerials and compositions in use. Patent applications WO9839379A1,WO9720207A1, and WO7901121A1 describe some more membrane methods.

The other major technique for separation is by using centrifugal forceapplied to the suspension solution causing separation depending on thespecific mass and gravities of the particles which compose the solution.The solution is contained in a chamber and rapidly rotated at highangular speed, which causes application of the centrifugal force. U.S.Pat. No. 6,315,707 and European patent application EP0520185A1 describecentrifugation methods. Another method, Field Flow Fractionation ismentioned in U.S. patent application UA20040011651A1. Here, the solutioncontaining the microparticles is made to flow through a separationchannel or chamber where an applied electric or thermal field causesfractionation or separation of the particles due to the field gradientacross the width of the channel. Depending on their charge ortemperature response, particles are drawn to the top or bottom of thechannel and the remaining solution can be suitably extracted. U.S.patent application US20040018611A1 deals with yet another method forparticle separation utilizing the effects of a High Gradient MagneticSeparation (HGMS). Particles are either tagged with magnetic particles,or simply subjected to a magnetic field and thus separated based ontheir magnetic response. Another technique to efficiently separate bloodcells from plasma is to cause aggregation of blood cells by exposure ofwhole blood to an ultrasonic standing wave as described in Cousins etal, “Clarification of plasma from whole human blood using ultrasound,”Ultrasonics, Vol. 38, 2000. When this is done, the cells concentrateinto clumps at radial separations of half wavelengths. The clumps growin size and sediment under gravity and a distinct plasma/cell interfaceforms as cells sediment.

However, centrifugation is too bulky for point-of-care handhelddetection equipment. It is laboratory specific and time-consuming.Magnetic separation and Field flow fractionation require the use ofspecialized equipment as does Ultrasonic separation. These techniquesare generally more expensive than the other methods. Membrane filtrationis suitable for disposable, point-of-care applications but the inherentproblems have been aggregation and fragility of materials. Thefabrication of the membranes and the subsequent integration of membranesinto existing devices can be a complicated process. It is alsorelatively more time-consuming. Furthermore, membrane filtrationtechniques are also more expensive and require high pressures and/orspecialized fluid driving.

No known technique has been able to achieve the characteristics ofbioparticle separation with an easy and low-cost method.

SUMMARY OF THE INVENTION

Certain embodiments of the present invention seek to address theshortcoming listed above. Disclosed herein are the techniques used foron-chip bioparticle separation using a series of pressure pulses and itsapplication for disposable biochips.

Disclosed herein is a novel filter-less separation technique forseparating suspended particles from solution. Embodiments of the presentinvention overcome many of the disadvantages of the prior art byproviding an on-chip bioparticle separator using a series of pressurepulses that is small in size, easy to fabricate, more reliable (since ithas no moving parts or complex control equipment), low cost, and has asimpler actuation/control circuit than conventional separationtechniques.

Specifically, disclosed herein is a novel on-chip bioparticle separatorusing a series of pressure pulses, one such pressure pulses having highamplitude and short duration, and which can be fabricated as a fullyintegrated component of a microfluidic biochemical analysis system,which is suitable for disposable, point-of-care applications.

Further disclosed herein are techniques to apply a series of pressurepulses to the microfluidic biochip. The bioparticle separator using aseries of pressure pulses is ideally suited towards microfluidicapplications and cart be easily controlled by changing a number ofparameters such as a number of pulses, pressure magnitude, rise and falltimes of the pressure pulses, and the duration of the pressure pulses(including multi-stage profile of pulses). Control of the pressureprofile characteristics can be achieved by any pressure source regulatedfrom a computer using programs such as LabVIEW™ or by using a dedicatedelectronic controller.

In accordance with an embodiment of the present invention, the choice ofthe pressure sources is a pressurized tank filled with biochemicallyinert gas, specifically nitrogen which does not react with any of thebiochemical microfluidic samples. However, as will be readily apparent,other gases may also be used for this application including in certaincases, gases (such as oxygen) which will actually promote (or impede) agiven biochemical reaction.

The bioparticle separator using a series of pressure pulses can beeasily fabricated and integrated on a wide variety of substratematerials typically used for biochip applications such as Silicon,Silicon derived surfaces such as Silicon Dioxide, Silicon Carbide orSilicon Nitride, Glass, injection molded or embossed polymer substrates,polymer laminates or thin films, and ceramics.

Without intent of limiting the scope of application of the presentinvention, the application of the present invention is generally alow-cost, disposable plastic biochip for biochemical analysis, whereinthe bioparticle separator is a fully integrated component of thebiochip.

Certain embodiments of the present invention overcome the deficienciesand inadequacies in the prior art as described in the previous sectionand as generally known in the industry.

Certain embodiments of the present invention provide a technique forbioparticle separation, from a suspension solution, wherein theaforementioned technique is fully compatible with the techniques andmethodology commonly used with biochips and can serve as afully-integrated portion of the biochip.

Also disclosed herein is a means of generating the requisite pressurepulses for achieving separation of bioparticles from a suspensionwherein the pressure generation system is not a part of the biochip, inaccordance with an embodiment of the present invention.

Further disclosed herein is a means of generating the requisite pressurepulses for achieving separation of bioparticles from a suspension,wherein the pressure generation system is a fully-integrated componentof the biochip, in accordance with an embodiment of the presentinvention.

Certain embodiments of the present invention achieve filter-lessseparation of bioparticles from suspension by using a plurality ofpressure pulses, wherein the amplitude, duration, nature and periodicityof the pressure pulses is altered to achieve separation.

Certain embodiments of the present invention provide a multitude ofpressure pulse profiles, which may be used for achieving separation ofbioparticles from a suspension.

Other features and advantages of the present invention will becomeapparent from the detailed description of various embodiments of thepresent invention when considered in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention, as defined in the claims, can be betterunderstood with reference to the following drawings and microphotographsof the actual devices. The drawings are not all necessarily drawn toscale, emphasis instead being placed upon clearly illustratingprinciples of the present invention.

FIGS. 1 a-1 g are a schematic illustration of the operation of theon-chip bioparticle separator using a series of pressure pulses inconjunction with a microfluidic system and also a schematic view of thepressure profile used therewith, in accordance with an embodiment of thepresent invention.

FIGS. 2 a-2 d show the various profiles of pressure pulses andcombinations thereof which maybe used for the separation process, inaccordance with certain embodiments of the present invention.

FIGS. 3 a-3 d show various architectures of the microfluidic channelstructures that may be used, in accordance with certain embodiments ofthe present invention.

FIGS. 4 a-4 b show schematic sketches illustrating the use of multipleinlets for applying the aforementioned pressure pulses and theirlocations with respect to the microfluidic channel network, inaccordance with certain embodiments of the present invention.

FIGS. 5 a-5 c show a schematic of the apparatus for the on-chipbioparticle separator wherein the pressure delivery system is notintegrated with the biochip, in accordance with certain embodiments ofthe present invention.

FIGS. 6 a-6 b show micro-photographs of a typical result of the on-chipbioparticle separator using a series of pressure pulses, in accordancewith an embodiment of the present invention.

FIGS. 7 a-7 b show characterization results of the on-chip bioparticleseparator using a series of pressure pulses, such as percentage ofsolution purged of bioparticles as a function of the number of pressurepulses, and as a function of the applied pressure pulses, in accordancewith certain embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Broadly stated, certain embodiments of die present invention provide anon-chip bioparticle separator for an aqueous suspension, by applying aseries of pressure pulses. Embodiments of the present invention use aseries of pressure pulses for separating bioparticles on demand.

A key concept disclosed herein is the use of a precisely defined seriesof pressure pulses to separate bioparticles from biofluid on abiocompatible plastic substrate. When these short-duration, pressurepulses are applied to a plug of biofluid, the viscous drag, inertialforce, and shear force on a particle inhibit it from achieving the samevelocity as the surrounding liquid. Hence, after a series of pressurepulses, the suspended bioparticles are separated in the rear or the headof the liquid column.

Definitions

The term “pressure pulse” as used herein describes a single or pluralityof precisely defined changes in pressure over a period of time deliveredby the pressure source. The pressure pulse can be controlled by anyelectronic, chemical, thermal, pneumatic pressure generator coupled to apower supply or by designing a specific pressure source to deliver thedesired characteristics. Furthermore, a wide variety profile of pressurepulses, such as the square wave pulse, half-square wave pulse, sine wavepulse, half-sine wave pulse, triangular pulse, half-triangular pulse,and multi-stage pulse, can be created by commonly available controllers.

The process of “Microfabrication” as described herein relates to theprocess used for manufacture of micrometer sized features on a varietyof substrates using standard microfabrication techniques as understoodwidely by those skilled in this art. The process of microfabricationtypically involves a combination of processes such as photolithography,wet etching, dry etching, electroplating, laser ablation, chemicaldeposition, plasma deposition, surface modification, injection molding,hot embossing, thermoplastic fusion bonding, low temperature bondingusing adhesives and other processes commonly used for manufacture ofMEMS (microelectromechanical systems) or semiconductor devices.“Microfabricated” or “microfabricated devices” as referred to hereinrefers to the patterns or devices manufactured using themicrofabrication technology.

The term “chip”, “microchip”, or “microfluidic chip” as used hereinmeans a microfluidic device generally containing a multitude ofmicrochannels and chambers that may or may not be interconnected witheach another. Typically, such biochips include a multitude of active orpassive components such as microchannels, microvalves, micropumps,biosensors, ports, flow conduits, filters, fluidic interconnections,electrical interconnects, microelectrodes, and related control systems.More specifically the term “biochip” is used to define a chip that isused for detection of biochemically relevant parameters from a liquid orgaseous sample. The microfluidic system of the biochip regulates themotion of the liquids or gases on the biochip and generally providesflow control with the aim of interaction with the analytical components,such as biosensors, for analysis of the required parameter.

The term “microchannel” as used herein refers to a groove or pluralityof grooves created on a suitable substrate with at least one of thedimensions of the groove in the micrometer range. Microchannels can havewidths, lengths, and/or depths ranging from 1 μm to 1000 μm. It shouldbe noted that the terms “channel” and “microchannel” are usedinterchangeably in this description. Microchannels can be used asstand-alone units or in conjunction with other microchannels to form anetwork of channels with a plurality of flow paths and intersections.

The term “microfluidic” generally refers to the use of microchannels fortransport of liquids or gases. The microfluidic system consists of amultitude of microchannels forming a network and associated flow controlcomponents such as pumps, valves and filters. Microfluidic systems areideally suited for controlling minute volumes of liquids or gases.Typically, microfluidic systems can be designed to handle fluid volumesranging from the picoliter to the milliliter range.

The term “substrate” as used herein refers to the structural componentused for fabrication of the micrometer sized features usingmicrofabrication techniques. A wide variety of substrate materials arecommonly used for microfabrication including, but not limited tosilicon, glass, polymers, plastics, and ceramics to name a few. Thesubstrate material may be transparent or opaque, dimensionally rigid,semi-rigid or flexible, as per the application they are used for.Generally, microfluidic devices consist of at least two substrate layerswhere one of the faces of one substrate layer contains the microchannelsand one face of the second substrate layer is used to seal themicrochannels. The terms “substrate” and “layer” are usedinterchangeably in this description. Specifically herein, the substrateis a material that can withstand the thermal dissociation temperature ofthe solid-propellant materials.

The intent of defining the terms stated above is to clarify their use inthis description and does not explicitly or implicitly limit theapplication of the present invention by modifications or variations inperception of the definitions.

On-Chip Bioparticle Separator Using a Series of Pressure Pulses

Certain embodiments of the present invention provide an on-chipbioparticle separation scheme for microfluidic devices, which needs tobe inherently suited to μTAS (Micro Total Analysis System). Also theseries of pressure pulses generated to separate the bioparticle frombiofluid should be precisely controlled. This approach gives the userfast and efficient results, avoids the use of specialized and bulkyequipment, and is suited for integration into microfluidic devices formass-production. This method allows the user to fabricate a functionalon-chip bioparticle separator in a number of forms such as films, sheetsand paste mixture along with an inert polymer.

Without wishing to be bound by a particular theory, generally speakingthe principle of operation of various embodiments of the presentinvention may be described as follows: very small particles ormicrospheres in a moving liquid suspension experience a force governedby Stokes Law. It is primarily based on the radius of the microsphereand the viscosity of the surrounding liquid. For very small Reynoldsnumber, Re, at the microfluidic level, the drag force on a microspherein suspension is expressed as Fd=6πμVd, where Fd is the drag force ofthe fluid on a sphere, μ is the viscosity of the fluid, V is thevelocity of the sphere relative to the liquid, and d is the radius ofthe sphere. In microfluidic devices, typically, the Reynolds number ismuch less than 1. At a very low Reynolds number, say Re=10⁻³, the dragon a microsphere depends greatly on its distance from the channel walls.Conversely, at a Reynolds number of 10⁴, the drag is independent of thatdistance.

During flow of the biofluid, the drag on an individual bioparticle willbe a function of its distance from the channel sidewalls. The closer thechannel sidewall to a bioparticle, the higher the drag force on thatbioparticle. The drag effect due to channel sidewall is specific only tomicrofluidic devices. In other words, the same drag effect would not bepresent in a macroscale device with much larger fluidic channels. Thusin microfluidic systems, suspended particles experience a high drag dueto the small channel dimensions. The Diffusion coefficient ofbioparticles plays an important role here. As described in J. Brody etal, SPIE, v 2978, 1997, the diffusion coefficients are inverselyproportional to the size of the particles. Larger particles will have asmaller diffusion coefficient and smaller particles will have relativelylarger diffusion coefficients. In addition, the shear rate on a particlein a suspension solution is proportional to the flow velocity of thesolution. This implies that as velocity increases, particles willexperience more shear drag and flow slower in relation to the rest ofthe surrounding liquid.

When a biofluid with bioparticles flows through a microchannel, thebioparticle will tend to move slower than the surrounding liquid. When aseries of short-duration, high pressure pulses are applied to the plug,the viscous drag, inertial force and shear force on a particle inhibitit from achieving the same velocity as the surrounding liquid. Hence,after a series of pressure pulses, the suspended bioparticles accumulatetowards the rear of the liquid column. So the speed and efficiency ofseparation is greatly improved with a series of pressure pulses, ascompared with the separation; achieved by application of continuouspressure. The primary features of this separation; system are a longmicrochannel preceded by a microdispenser to reliably dispense a knownvolume into the microchannel upon which the pressure pulses can beapplied.

A schematic sketch explaining the operation of an embodiment of theon-chip bioparticle separator using a series of pressure pulses is shownin FIG. 1 a to FIG. 1 f. FIG. 1 a and FIG. 1 b show the basic schematicof microdispenser structure where a biofluid with bioparticles 110 isintroduced via a biofluid inlet 102, into a reservoir 106. A series ofpressure pulses is applied through the pressure inlet 100 and pushesbiofluid in the microchannel 108 toward the outlet port 104.

For operation, biofluid with bioparticles 110 is introduced into thebiofluid inlet 102 at very low pressure. It enters the reservoir 106 andis prevented from exiting in the microchannel 108. The pressure inlet100 has much smaller dimensions than the channel, and the biofluid isthus prevented from entering the pressure inlet 100 due to an availablepath of lesser resistance leading to the reservoir 106. FIG. 1 c throughFIG. 1 e show a schematic sketch explaining the concept of bioparticleseparation. As shown in FIG. 1 b, the reservoir 106 is initially loadedwith a biofluid with bioparticles. A precisely graduated volume of thisbiofluid is then ejected from the reservoir 106 at low velocity toensure that no fluidic residue is left behind in reservoir 106 as shownin FIG. 1 c. Next, a series of high pressure, short duration pulses 146are applied to this liquid plug. As shown in FIG. 1 c, FIG. 1 d, andFIG. 1 e, a series of pressure pulses causes the plug 120 to move andthe bioparticles to accumulate towards the rear end of the liquid plug140. FIG. 1 f also shows a detailed view of the separation ofbioparticles. FIG. 1 g shows a schematic sketch of the series of appliedpressure pulses. Note that the initial low pressure pulse (prior to t₀,is used for dispensing the biofluid out of the reservoir 106, andthereafter a series of high magnitude, short duration pulses are appliedfrom t₁ to t₂ wherein these times correspond to the schematic sequencesof FIG. 1 d and FIG. 1 e.

FIGS. 2 a-2 d show various profiles that can be used for the series ofpressure pulses for an on-chip bioparticle separator. As shown in FIG. 2a, in accordance with an embodiment of the present invention, the shapeof the series of pressure pulses is an approximately triangular pulse,which consists of magnitude 204, a rising section 206, a falling section208, the on-time of the pulse 210, the peak-to-peak duration between thepulses 202, and the number of the pressure pulses 212. In accordancewith an embodiment of the present invention, pressure pulses withmagnitude 204 of approximately 5 KPa to 50 KPa (kilo Pascal) andpeak-to-peak duration 202 of approximately 20 msec to 200 msec(milliseconds) are used. Residual pressure between each pulse is bledoff in this duration. For a sequence of 10 to 50 pulses, the desiredseparation can be achieved in 5 to 150 sec.

In accordance with another embodiment of the present invention, theshape of the series of pressure pulses is rectangular, which consists ofthe pressure magnitude 216, the duration of the pulses 214, the numberof the pressure pulses 222, and the same and/or different on-time ofpulse 218, 220, as shown in FIG. 2 b. In yet another embodiment, a moregeneric type of pressure pulses can be applied for the on-chipbioparticle separator, which is called the multi-stage pressure pulse.It has the pressure magnitude 224, various rising slopes 226, 228, 230and various falling slopes 232, 234, 236 with respect to their duration240, 242, 244, 246, 248, 250, and 252 respectively, the duration betweenthe pulses 254, and the number of the pulses 256, as shown in FIG. 2 c.In yet another embodiment a combination of the different type ofpressure pulses, for instance, triangular 260 and/or rectangular 262and/or generic type pulses 264 with various magnitudes 266, 268, 270 maybe applied. The applied pressure pulse may also have the same and/ordifferent duration between pulses 272, 274, for the total number ofpulses 276.

The various cross-sections of the microchannel that can be used include,but are not limited to, rectangular or circular or trapezoidal, and soon. For a hydrophobic substrate with a rectangular cross-section of themicrochannel, when a liquid encounters an abrupt change in channelwidth, from large to small, a positive pressure is required to push theliquid across the restriction. As described in C. Ahn et al, μTAS, 2000,this pressure can be given: ΔP=2σ cos(Θc) [(1/w1 +1h1)−(1/w2 +1/h2)],wherein; w1, h1 and w2, h2 are the width, height of the widemicrochannel and the narrow microchannel respectively, Θc is the contactangle, σ is the surface tension of the liquid/air interface and ΔP isthe pressure required to push the liquid into the narrow channel. Thegeometry of the reservoir decides the volume of dispensed liquid. Inaccordance with an embodiment of the present invention, the volume ofthe reservoir ranges from 10 nanoliter to 10 microliter as determined bythe volume of the reservoir. The passive valve at the outlet of thereservoir is 40 μm wide and the following microchannel is approximately50 μm in depth and 1 mm in width. The total length of the microchannelis from 10 cm to 100 cm.

Some of the microfluidic components that can be used especially include,but are not limited to, a wide variety of valves such as passive and/oractive valves and dispensers. FIG. 3 a shows a series of passive valves310 incorporated into the microchannels, which provide for a rapid risein flow velocity when the liquid, upon exiting from the passive valve,enters into the wider microchannel. This would be expected to provide aflow ‘spike’. In accordance with an embodiment of the present invention,the distance between two successive passive valves is 1/10^(th) to½^(th) of plug length, wherein the plug length is defined as the lengthoccupied by the liquid column as it is ejected from the dispensingreservoir 306 and fills the subsequent microchannel 308. It is expectedthat each valve would provide a spike in the flow rate of the liquidflowing through it. With a series of such spikes in flow rates, it isenvisaged that separation could possibly be achieved with a single largepressure pulse or with constant pressure flow. The passive valves canrange in width from approximately 10 to 490 micrometers, when themicrochannel is approximately 500 micrometers wide.

In another embodiment of the present invention, the various shapes ofthe microchannel 308 that may be used include, but are not limited to, arectangular-spiral shape, as shown in FIG. 3 b, or a circular- or anoval-spiral shape or a triangular-spiral shape, and so on. In anotherembodiment of the present invention, the combination of various shapesof the microchannel with each section of different width can be used,such as a part of the microchannel with increasing and/or decreasingchannel widths 312, 314, a sine-wave-like channel 316, and so on, asshown in FIG. 3 c, including a reservoir 304 which can be used to gatherbioparticles after separation, and especially a packed bed column 310 bya dense porous nano/micro-structure 322 through the microchannel 308, ofwhich the morphology is very useful as preconcentrators andmicroreactors as well as chromatographic separation columns in chemicaland biological application, as shown in FIG. 3 d.

In yet another embodiment of the present invention, a plurality oflocations for applying a series of pressure pulses may be used. FIG. 4 ashows one of the examples of various locations for pressure inlets 400,408, 410, 412. Furthermore, in yet another embodiment of the presentinvention, a series of negative pressure pulses 426, as shown in FIG. 4b, may be used for the scheme of a filter-less bioparticle separator. Abiofluid sample in the reservoir 406 which is injected through thebiofluid inlet 400 can be “pulled out” by a series of negative pressurepulses 426 applied at the pressure inlet 422. Furthermore, as shown inFIG. 4 b, an additional reservoir 416 may be used to collect the “frontend” of the suspension, which is purged of microparticles, and by usingpositive pressure at yet another pressure inlet 416, this solution maybe transferred to a separate outlet 420.

Some of the substrate materials that may be used include, but are notlimited to, Silicon or a derived Silicon surface such as Silicon dioxideor Silicon Nitride, glass, quartz, ceramics, a wide variety of polymerssuch as PDMS, PMMS, PC, COC, or a combination of listed substrates suchas a glass substrate with a coated film of PMMA on the surface. Inaccordance with an embodiment of the present invention, a low-costplastic surface is used for fabricating the on-chip bioparticleseparator using a series of pressure pulses for a disposable biochip.The substrate material may have a thickness ranging from 100 μm to 5 mm.The thickness of the substrate material should be sufficient to impartdimensional stability required for the various steps of themicrofabrication process. Generally, the surface has a hydrophobicsurface characteristic specifically for the passive microfluidicdispensing schemes. The concepts of the passive microvalves and theon-chip dispensers are clearly detailed in U.S. Provisional PatentApplication 60/204,214 filed on May 12, 2000, U.S. Provisional PatentApplication 60/209,051 filed on Jun. 2, 2000, and U.S. patentapplication Ser. No. 10/602,575 filed on Jun. 24, 2003, all of which areincorporated herein by reference in their entirety. The surfaces of theabove listed substrates may be easily modified by a variety of surfacemodifications techniques such as plasma treatment, plasma deposition,covalent cross-linking etc. that are well known in the art. Depending onthe application, the biocompatibility characteristics of the substratemay be an important factor in determining choice of substrate material.Broadly stating, any substrate material that can be handled usingestablished microfabrication processes may be used.

The apparatus for generating a series of pressure pulses is designedwith the facility to apply a desired pressure for a desired timeduration to the pressure inlet of the biochip. FIGS. 5 a-5 c show theschematic of the apparatus, in accordance with certain embodiments ofthe present invention. As shown in FIG. 5 a the precision driving screws516, 518 are gradually rotated to build pressure in the syringes 512,514. The chambers of the syringes are directly connected to the inletsof pressure sensors 508, 510 with a sensing range of 0 to 50 kPa. Theoutlets of the syringes lead to inlets of solenoid valves 502, 504. Thevalves 502, 504 are either on (open) or off (closed). With no power, thevalves are normally off, that is, closed. The outlets of the valves leadto a chamber (common point) at which another pressure sensor 520 isconnected. This sensor 520 is meant to provide a reading of the actualpressure applied to the pressure inlet of the on-chip bioparticleseparator. In another embodiment, as shown in FIG. 5 b, ahigh-pressurized tank 516 of approximately 450 to 3000 psi, one and/ormore than one regulators) 518, 520 for decreasing pressure, electricallymotivated flow control valves 524, 526 and precision pressure sensors522, 528 for monitoring and/or feedback control may be used. In yetanother embodiment, FIG. 5 c shows precision pressure pulse arrays 536,538 located at appropriate positions along the microchannel 518. Inthese arrays a suitable solid-propellant material 540 can be depositedand connected through microchannel branches 542. The use of solidpropellants for on-chip microfluidic manipulation is disclosed in U.S.Patent application having attorney docket number 200057.00011,incorporated herein in its entirety by reference.

The control apparatus has a DAQ (Digital Acquisition) board to interfacewith the control software. In accordance with an embodiment of thepresent invention, PC based control software such as LabVIEW™ is used toprovide a graphical user interface (GUI) to read data from pressuresensors and control operation of valves in real-time. The interface hasprovision to control the on/off condition of each solenoid valve. Theon-time and duration for each valve may be specified. For example, if avalve needs to be turned on or opened at 5 seconds after start ofprogram, the on-time is entered as 5000 ms. If the valve needs to beheld open for 100 ms and then closed, off-time is entered as 5100 ms.This means the valve will open at 5000 ms from the start of program, andclose at 5100 ms from the start of program, providing an open time of100 ms. The readouts of pressure sensors are also displayed inreal-time. The reading from the pressure sensors may be simultaneouslystored in a text file for later analysis if needed. There is a provisionfor ‘looping’ the program, which is useful when the cycle needs to berun multiple times for delivering a series of pressure pulses. Inanother embodiment, some of the pressure systems that may be usedinclude, but are not limited to pressurized tanks, or a micro sized pumpsuch as solid and/or liquid propellant, or a precision detonator togenerate pressure pulses, or a dedicated ASIC as an interfacecontroller.

Microphotographs as test results of the front end and rear end of thesuspension solution plug in the microchannel 610 are shown in FIGS. 6a-6 b. As FIG. 6 a clearly shows, the front end 604 of the solution plug608 is purged of bioparticles while bioparticles 612 are accumulated atthe rear end 614 in flow direction 602 as shown in FIG. 6 b. Themovement of the liquid plug through the microchannel and the separationof the bioparticles are visually monitored using a high resolutionmicroscope, along with a scale to measure the length of liquid plugcleared of bioparticles. The total length of the dispensed biofluid plugand the length of liquid visibly clear of bioparticles are measured tocalculate the volume of liquid purged of bioparticles. After applying adesired number of pulses, the device is taken under a high-resolutionmicroscope and the length of liquid column visibly free of beads wasmeasured as a percentage of the total length of dispensed solution.

Characterization results are shown in FIGS. 7 a-7 b. FIG. 7 a showsthat, for a given pressure, increasing the number of pulses results inmore separation. The final degree of separation is directly proportionalto the number of pressure pulses. This is true only until maximumachievable separation, or separation saturation, is reached. Once thatlevel of separation is reached, applying pressure pulses further doesnot increase the degree of separation any more. For higher inputpressures, the maximum separation is achieved with a lower number ofpulses. As shown in FIG. 7 b, with a low number of applied pulses, theinlet pressure has a significant impact on the separation achieved.However, for a very large number of pulses, the percentage separation isessentially independent of pressure and maximum achievable separation isseen at low pressure. A desired dynamic pressure characteristic can berealized by optimizing the inlet pressure and number of pulses toachieve maximum separation in a relatively short time.

Certain embodiments of the aforementioned on-chip bioparticle separatorusing a series of pressure pulses offers numerous advantages formicrofluidic manipulation, a few of which are enumerated hereafter.

Certain embodiments of the present invention provide the ability tofabricate a fully integrated separation mechanism for microfluidicchips.

Certain embodiments of the present invention provide the ability tofabricate an integrated separator without using complex fabricationtechniques.

Certain embodiments of the present invention provide ease of integrationwith a disposable microfluidic system.

Certain embodiments of the present invention realize a reliableactuation scheme due to lack of bulky parts in the pressure source,wherein solid propellant based actuators are used as an on-chip pressuresource.

Certain embodiments of the present invention provide the ability togenerate rapid separations of bioparticles from suspensions for amicrofluidic biochip.

While the invention has been described with reference to certainembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted withoutdeparting from the scope of the invention. In addition, manymodifications may be made to adapt a particular situation or material tothe teachings of the invention without departing from its scope.Therefore, it is intended that the invention not be limited to theparticular embodiment disclosed, but that the invention will include allembodiments falling within the scope of the appended claims.

1. A method to separate particles suspended in a fluid, said methodcomprising: loading a micro-dispenser with a predetermined volume ofsaid fluid containing said suspended particles; ejecting saidpredetermined volume of said fluid containing said suspended particlesfrom said micro-dispenser into a micro-channel of substantially constantdiameter to form a liquid plug within said micro-channel, said liquidplug having a first end and a second end; and applying at least onepressure pulse to said liquid plug within said micro-channel to causesaid liquid plug to move along said micro-channel and said suspendedparticles to accumulate toward said first end of said liquid plug. 2.The method of claim 1 wherein said loading comprises applying said fluidcontaining said suspended particles to an inlet port of saidmicro-dispenser.
 3. The method of claim 1 wherein said ejectingcomprises releasing a first volume of pressurized gas at a firstpressure level into an inlet port of said micro-dispenser for a firstpredetermined period of time.
 4. The method of claim 3 wherein saidapplying at least one pressure pulse comprises releasing a second volumeof pressurized gas at a second pressure level into said inlet port ofsaid micro-dispenser for a second predetermined period of time.
 5. Themethod of claim 4 wherein said second pressure level is greater thansaid first pressure level.
 6. The method of claim 4 wherein said secondpredetermined period of time is less than said first predeterminedperiod of time.
 7. The method of claim 1 further comprising tapping off,from an outlet port of said micro-channel, a portion of said liquid plugthat is toward said second end of said liquid plug and that is free ofsaid suspended particles.
 8. The method of claim 7 further comprisinganalyzing said portion of said liquid plug to determine at least onecharacteristic of said portion of said liquid plug.
 9. The method ofclaim 1 wherein said fluid comprises whole blood.
 10. The method ofclaim 1 wherein said suspended particles comprise blood cells.
 11. Themethod of claim 7 wherein said, portion of said liquid plug comprisesblood plasma.